As an example of a three-layer substrate configured to interpose a glass substrate, there is a conventional pressure sensor of a three-layer structure including a sensor chip (silicon substrate), a glass base, and a silicon tube. In the pressure sensor of the three-layer structure, the sensor chip, the glass base, and the silicon tube are bonded to each other by anodic bonding (see PTL 1, for example).
Anodic bonding is a direct bonding method that does not interpose a third material between bonded members. When glass including movable ions (metal positive ions such as Na+ or K+) is laminated with silicon or metal and high temperature and high voltage are applied, an electrostatic attraction is exerted on the interface, covalent bonding occurs, and both members are bonded to each other. This technique is used to bond a sensor chip, glass base, and silicon tube to each other to obtain a pressure sensor of a three-layer structure. The heating temperature at which the bonded part is heated during anodic bonding is referred to as the bonding temperature.
[First Anodic Bonding (Primary Anodic Bonding)]
First, as illustrated in FIG. 3, a glass base 12 is superposed on a silicon tube 13, the upper surface of the glass base 12 is connected to the negative electrode (cathode) and the lower surface of the silicon tube 13 is connected to the positive electrode (anode), and a high voltage is applied when the bonding temperature is reached to perform anodic bonding between the glass base 12 and the silicon tube 13. This forms a bonded body (glass base/silicon tube bonded body) 14 of the glass base 12 and the silicon tube 13.
[Second Anodic Bonding (Secondary Anodic Bonding)]
Next, as illustrated in FIG. 4, a sensor chip (silicon substrate) 11 is superposed on the glass base/silicon tube bonded body 14 and the upper surface of the sensor chip 11 is connected to the positive electrode (anode), the lower surface (lower surface of the silicon tube 13) of the glass base/silicon tube bonded body 14 is connected to the negative electrode (cathode), and a high voltage is applied when the bonding temperature is reached to perform anodic bonding between the sensor chip 11 and the glass base/silicon tube bonded body 14. This forms a bonded body (sensor chip/glass base/silicon tube bonded body) 15 of the sensor chip 11 and the glass base/silicon tube bonded body 14 and provides a pressure sensor 200 of a three-layer structure.
As a method for manufacturing the pressure sensor 200, there is a method that bonds a wafer (sensor chip wafer) in which a plurality of sensor chips 11 are created, a wafer (glass base wafer) in which a plurality of glass bases 12 are created, and a wafer (silicon tube wafer) in which a plurality of silicon tubes 13 are created to form a bonded body having the three wafers, cuts the bonded body having the three wafers using dicing, and obtains a plurality of pressure sensors 200 in order to efficiently manufacture many pressure sensors 200.